The aims of the project are twofold: (1) to prepare folate analogues containing fluorescent and photoreactive substituents and evaluate them as probes of dihydrofolate reductase structure and function as well as probes of the mechanism of one-carbon reduced folate (FAH4C-1) transport into cells. The specific problems to be investigated include: (a) synthesis of lysine and ornithine analogues of amethopterin containing fluorescent and photoaffinity substituents; (b) fluorescence binding and photolabeling studies of dihydrofolate reductases; (c) fluorescence binding (and/or transport) and photolabeling studies of the FAH4C-1 membrane transport receptor complex on intact murine L1210 cells and on the receptor complex isolated in the presence of detergent and purified by affinity chromatography; (d) covalent labeling of the folate analogue membrane receptor complex in L1210 cells with a radiolabeled photoaffinity analogue of amethopterin and determination of the receptor binding site amino acid sequence using [35S] phenylisothiocyanate in the structural studies; and (2) the synthesis of a series of analogues of aureusidin, a natural product which is a potent inhibitor of iodothyronine deiodinase. Undergraduate research participants will be involved in the planning, synthesis, purification, and characterization of the analogues. It is expected that being involved in a fundamental research project of this type will improve the students' understanding of chemistry, motivate them toward careers as chemists, and enhance their position when applying to graduate school or industry.